1. Field of the Invention
The present invention relates to an apparatus for extracting cores, in particular apparatus comprising an outer tube which may be joined to a set of bore rods or is formed by a part thereof and which may be fitted or provided at its lower end with a core bit or the like, an inner tube which may be fitted or provided at its lower end with a core bit or the like and contains a core receiving space, and a striking device which may be driven by rotation of the outer tube and which comprises a hammer and an anvil for producing a periodic axial movement of the inner tube relative to the outer tube.
Using such an apparatus, it is possible to extract cores or appropriate samples which give useful results, even under unfavourable conditions, for example in the case of soft or varying formations.
2. Description of the Prior Art
German Offenlegungsschrift No. 1 634 490 describes apparatus which has a thread at its upper end, and by means of this thread it may be screwed into the lowermost rod of a set of bore rods. When extracting a core the whole set of rods must be drawn out in order to be able to remove, at the surface, the core from the apparatus attached to the lower end of the rods. This is complicated and time-consuming.